Paul Ehrenfest

Austrian physicist, 1880-1933

Ehrenfest made major contributions to the field of statistical mechanics and its relations with quantum mechanics, including the theory of phase transition and the Ehrenfest theorem. His name is also given to the Ehrenfest paradox, an apparent paradox in relativity still discussed today, to the Ehrenfest model, and to Ehrenfest time, the time characterizing the departure of quantum dynamics for observables from classical dynamics. Ehrenfest was particularly close to both Einstein and Bohr. Ehrenfest invited them over to Leiden in 1925, in an attempt to reconcile their scientific differences about the emerging quantum theory.

Source: Wikipedia

Ehrenfest, Paul

Atomphysiker (1880-1933). Autograph postcard signed, and with some mathematical calculations. Leiden. 2 SS. (Qu.-)8vo. Mit eh. Adresse und wiederholtem Namenszug im Absender.
$ 5,086 / 4.500 € (73836/BN47730)

In German, thanking the mathematician David Hilbert for sending him his latest scientific treatise, and mentioning his current preoccupation with Einstein's theory: "[...] At the moment I am extremely impatient to get to know your proof of Theorem I [...]". - Small loss of singular letters through punched holes, otherwise in good condition.

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Ehrenfest, Paul

3 eigenh. Briefe mit U. und 1 Originalphotographie.
Autograph ist nicht mehr verfügbar

Friendly correspondence with a Natasha who at that time was apparently close to Ehrenfest's wife Tatjana. Ehrenfest promises to write to both of them, goes on to develop some thoughts on mechanics and physics, and wants them to ask Joffe, Frenkel, Bursian, Krutkov, and Friedmann in case they do not understand what he has written. He encourages Natasha not to become frustrated by her own scientific work , since "everyone who has become involved with science faces the same problems [...] You should see how Bohr and Einstein were tormented [...]" (transl.). - The picture shows Ehrenfest with some of his students.